A "small number" of employee Macs were involved and the attack came after they visited "a website for software developers that transmitted the malicious computer code," according to the report. Apple is working with law enforcement "to find the source of the so-called malware," the WSJ reported.

The malware is thought to be the same that hit Facebook Inc. employees last month, according to the report, and both companies say no data was stolen.

Bloomberg reported that both of these attacks are suspected to be part of a series of 40 attacks on U.S. companies coming from Eastern Europe. The hackers "appear to be seeking company secrets, research and intellectual property they can sell underground," according to the report.